Flat panel displays are widely used in a variety of applications, including computer displays. One suitable flat panel display is a field emission display. Field emission displays typically include a generally planar emitter substrate covered by a display screen. A surface of the emitter substrate has formed thereon an array of surface discontinuities or "emitters" projecting toward the display screen. The emitters are conical projections which may be integral to the substrate. Typically, contiguous groups of emitters are grouped into emitter sets in which the emitters in each emitter set are commonly connected.
The emitter sets are typically arranged in an array of columns and rows, and a conductive extraction grid is positioned above the emitters. The extraction grid includes small openings into which the emitters project. All, or a portion, of the extraction grid is driven with a voltage of about 30-120 V. Each emitter set is then selectively activated by applying a voltage to the emitter set The voltage differential between the extraction grid and the emitter sets produces an electric field extending from the extraction grid to the emitter set having a sufficient intensity to cause the emitters to emit electrons.
The display screen is mounted directly above the extraction grid. The display screen is formed from a glass panel coated with a transparent conductive material that forms an anode biased to about 1-2 kV. The anode attracts the emitted electrons, causing the electrons to pass through the extraction grid. A cathodoluminescent layer covers a surface of the anode facing the extraction grid so that the electrons strike the cathodoluminescent layer as they travel toward the 1-2 kV potential of the anode. The electrons striking the cathodoluminescent layer cause the cathodoluminescent layer to emit light at the impact site. Emitted light then passes through the anode and the glass panel where it is visible to a viewer. The light emitted from each of the areas thus becomes all or part of a picture element or "pixel."
The brightness of the light produced in response to the emitted electrons depends, in part, upon the rate at which electrons strike the cathodoluminescent layer. The light intensity of each pixel can thus be controlled by controlling the current available to the corresponding emitter set To allow individual control of each of the pixels, the electric potential between each emitter set and the extraction grid is selectively controlled by a column signal and a row signal through corresponding drive circuitry. To create an image, the drive circuitry separately establishes current to each of the emitter sets.
To produce the intense electric field that extracts electrons from the emitters, the openings into which the emitters project are very small. Consequently, the distances between the emitters and the grid sections are very short. If the voltage differential between the emitters and the grids is too high, electrons will be extracted from the emitters at a rate that is sufficient to damage the emitters. Such high differential voltages can occur during packaging and handling due to statically induced charge on either the emitters, the extraction grid or the anode.